The present invention relates to a forward and backward movement mechanism (referred to as "movement mechanism" hereinafter) which enables the assembly of a long column or the like by extension without increasing the weight thereof.
A movement mechanism using a hydraulic cylinder and a screw rod is generally widely used in the fields of a telescopic boom of a crane, a telescopic column, a jack and the like.
The known movement mechanism is designed so that the buckling strength of a forwardly and backwardly moving member (referred to as "moving member" hereinafter) is born by the constituent members themselves such as a cylinder, a rod, a screw rod and the like, which constitute the movement mechanism. The movement mechanism also has no means for enforcing these members. If a movement mechanism having a long moving length is formed, the weight of the mechanism is inevitably increased. Although a movement mechanism having a long moving length can be theoretically produced, practical problems with respect to the weight, portability, containment properties and the like cannot be solved.
A jib crane using the known movement mechanism has an extension length of about 20 to 30 m. However, such a crane is a type that it is loaded on an exclusive carriage track or crawler transporter. In the present situation, a screw rod type jack has a lifting amount of several m in balance between the backward length of the screw rod and the depth of the receiving pit.
This is because since no means is provided for the buckling strength of the conventional movement mechanism for a telescopic movement in spite of the most importance of the buckling strength for design of a slender structure, the dead weight of the mechanism is inevitably excessively increased. Although there is demand for a convenient, long and portable telescopic column, such a telescopic column has not been realized so far.
However, it is thought that a movement mechanism which enables the realization of a moving length extremely longer than that of a conventional mechanism without increasing the weight and which can be contained in a compact case is very useful for various industrial fields because a work of supporting a load at a height and a work of lifting a load to a height can be easily realized by such a mechanism.